Cities 114 (2021) 103196 Contents lists available at ScienceDirect Cities journal homepage: www.elsevier.com/locate/cities Perceptions on barriers and opportunities for integrating urban agri-green roofs: A European Mediterranean compact city case Perla Zambrano-Prado a, b, *, 1, David Pons-Gumí a, 1, Susana Toboso-Chavero a, c, Felipe Parada a, Alejandro Josa d, Xavier Gabarrell a, c, Joan Rieradevall a, c a Sostenipra Research Group (Sostenipra 2017 SGR 1683), Institut de Ciència I Tecnologia Ambientals (ICTA-UAB), Universitat Autònoma de Barcelona, 08193 Cerdanyola del Vallès, Barcelona, Spain b Department of Techniques and Construction, Art Architecture and Design University Center, (CUAAD), University of Guadalajara (UdeG), Calzada Independencia Norte 5075, Huentitán El Bajo, 44250 Guadalajara, Mexico c Department of Chemical, Biological and Environmental Engineering, Universitat Autònoma de Barcelona (UAB), Campus UAB, 08193 Bellaterra, Barcelona, Spain d Department of Civil and Environmental Engineering (DECA), Civil Engineering School (Escola de Camins), Universitat Politècnica de Catalunya - BarcelonaTech (UPC), Jordi Girona 1-3, Building D2, 08034 Barcelona, Spain A R T I C L E I N F O A B S T R A C T Keywords: The main objective of this study is to analyze the perceived barriers and opportunities with regard to the Rooftop agriculture implementation of urban agri-green roofs (UAGR) in cities. The case study was conducted in Barcelona, a Stakeholders perception Mediterranean compact city. The World Café method was used in this work. Five categories of barriers and World Café opportunities were discussed (social, environmental, legal/administrative, technological/architectural, and Building economic) by interdisciplinary stakeholders. A total of 129 barriers and opportunities were identified. The main barriers identified were as follows: the lack of information and social cohesion regarding UAGR projects; the Mediterranean climate; the lack of specific regulations and protocols; the initial investment; and the pre-condition of the roof and its load bearing capacity. The main opportunities were social cohesion; improved life quality; new specific regulations; the profits derived from UAGR projects; and aesthetic improvement. The UAGR’s scale of impact results showed a homogeneous distribution between “building” and “city”, while the “global” scale remains residual. Regarding the stage of the UAGR life cycle at which barriers and opportu­ nities emerge, the results highlight how most opportunities appear during the “use” stage of the roof, whereas barriers do so during the “project” stage. 1. Introduction island (UHI) effect; specifically, temperatures in urban areas can be up to 5–12 ◦ C warmer compared to surrounding rural areas (Lee et al., 2014), The global population has increased rapidly since 1950. According to contributing to climate change. the projections, 68% of the world’s population will live in cities by 2050 Apart from the above-mentioned problems, cities with high popu­ (United Nations, 2018). lation density, the so-called compact cities, also experience important Urban areas have increased the pressure and exploitation levels issues related to a lack of space and more specifically green spaces. In imposed on the ecosystems both at local and global scale as they are this sense, real estate speculation, increased population density, spatial responsible directly or indirectly for approximately 75% of global en­ limitations, and the high competition in relation to land in urban areas ergy consumption and 80% of greenhouse gas (GHG) emissions (Ash have implicitly led to a decrease in the available green space surface per et al., 2008), exerting high impacts on levels of atmospheric pollution capita, demonstrating the need for new strategies to compensate for that and the rising demand for natural resources (Cerón-Palma et al., 2012). deficit (Tappert et al., 2018). Given the multiple benefits at the social, In addition, the built urban environment contributes to the urban heat economic, and environmental levels provided by green spaces and the * Corresponding author at: Sostenipra Research Group (Sostenipra 2017 SGR 1683), Institut de Ciència I Tecnologia Ambientals (ICTA-UAB), Universitat Autònoma de Barcelona, 08193 Cerdanyola del Vallès, Barcelona, Spain. E-mail address: perla.zambrano@academicos.udg.mx (P. Zambrano-Prado). 1 Perla Zambrano-Prado and David Pons-Gumí contributed equally to this paper and share first authorship. https://doi.org/10.1016/j.cities.2021.103196 Received 20 December 2019; Received in revised form 17 January 2021; Accepted 19 March 2021 Available online 2 April 2021 0264-2751/© 2021 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). P. Zambrano-Prado et al. Cities 114 (2021) 103196 growing concern with regard to the creation of sustainable cities to­ green roofs or solar panels in all new buildings located in commercial wards an improved quality of life, there is significant interest and need zones (The Guardian, 2015). to enhance such spaces (Taylor & Hochuli, 2017); however, the spatial Other cities around the world also have adopted bylaws on the limitations and high competition in cities for space make opportunities construction of green roofs on new buildings, Toronto (Canada) was the for greening increasing difficult. In this sense, rooftops are relevant to first city in North America to integrate these bylaws (City of Toronto, the transformation from underused spaces to green and productive 2009). In Asia, the city of Tokyo requires green roofs on both private and spaces (Toboso-Chavero et al., 2018). public buildings (C40 Cities, 2015). More recently, in South America, the cities of Guarulhos and Recife in Brazil and Cordoba in Argentina 1.1. Rooftop urban agriculture functionalities and experiences in cities also required green roofs (Grant & Gedge, 2019; Law No 7031, 2012; Liberalesso et al., 2020). Rooftop urban agriculture (RUA) in cities with high population Regarding policies for integrating RUA, New York City, Washington densities has multiple functionalities: it generates new agricultural DC, Chicago, Toronto, Singapore, and Paris initiated pioneer programs spaces, represents an alternative to the current value chains about related to food production on building rooftops. The NYC council meeting the demand for food in urban areas, and serves as an ideal tool included the use of rooftops for food production in local plans (The New to cover cities’ food needs by improving a city’s self-sufficiency, York City Council, 2010). Chicago reformed city laws regarding UA, reducing its dependence on foods that must be shipped in from a dis­ allowing urban farms on rooftops (City of Chicago, 2020; Urban sus­ tance and the derived costs and contribute to a more circular urban food tainability exchange, 2011). In Singapore, urban planners included production system and developing a fundamental role in other areas of rooftop farms in the definition of urban green spaces and diversified the city life (Nadal, Cerón-Palma, et al., 2018; Sanyé-Mengual et al., 2016). classification of agriculture land use, allowing this activity in urban Further, its benefits can be extended to addressing issues of psycholog­ areas (Diehl et al., 2020). Through the Parisculteurs program, Paris ical and physical health, social cohesion, economic development, urban supports rooftop urban agriculture projects, and more than 48 projects and landscape planning, and sustainability (Azunre et al., 2019; Cerón- have been developed on both public and private buildings since the first Palma et al., 2012; Sanyé-Mengual et al., 2016; Specht & Sanyé-Men­ call in 2016 (Ville de Paris, 2019). The Barcelona city Council promoted gual, 2017). It also has a relevant impact in terms of increasing biodi­ The First Green Roof Contest in 2017. Winning projects received a versity and habitats that are more suited to the life of flora and fauna in subsidy up to 75% of the construction cost. The requirements stipulated cities, creating green spaces and serving as an ideal tool for education that a minimum of 50% of the roof area or 200 m2 had to be green, and environmental awareness. Furthermore, increasing green spaces in especially (but not only) on residential roofs. Subsidies were not cities by implementing RUA has been demonstrated to be one of the key restricted to the integration of ornamental plants, and projects could approaches for mitigating UHI effects (Alexandri & Jones, 2008; Lee also integrate food production, rainwater harvesting, and renewable et al., 2014; Susca et al., 2011). In addition, RUA decreases energy energy systems (Barcelona City Council, 2017). consumption due thermal properties and insulating effects, creating As we can observe, cities worldwide are adopting green roof policies, energy savings for both cooling and heating buildings (Muñoz-Liesa especially North Europe, North America, and some Asian cities. In the et al., 2020; Nadal, Oriol, et al., 2018; Susca et al., 2011). case of South Europe, information in the literature regarding policies to support RUA projects are lacking. In Barcelona, recent subsidies have 1.2. City policies: green and urban agriculture roofs been emerged to encourage the implementation of these types of pro­ jects. However, the lack of promotion, specific laws, legal procedures, Due to the multiple benefits from green roofs (GR), urban policies and urban codes can act as barriers to integrate these policies in cities have been implemented in a global context, and the most representative that recently started to adopt support. incentive policies correspond to subsidy (53%) and adopting bylaws (15%). Most of these policies are presented in European cities (79% 1.3. Approach for identifying green roofs and rooftop urban agriculture subsidy and 23% bylaw) and North American and Asian cities (12% and barriers and opportunities 9% subsidy and 32% bylaw) (Liberalesso et al., 2020). Regarding North Europe, in 1996, the city of Basel (Switzerland) As observed in the last section, legal barriers, such laws, and started to promote green roofs via subsidy programs (Climate adapt, administrative procedures, are an important issue regarding RUA 2015). In the Netherlands, several municipalities support the construc­ implementation. In addition to legal barriers, others barriers and op­ tion of green roofs requiring minimum criteria to be able to apply for portunities, such as social, environmental, economic, aesthetical, and subsidies (Almelo, 2020; Amstelveen, 2019; Amsterdam, 2020; Den technological barriers, have been identified (Cerón-Palma et al., 2012; Bosch, 2020; Groningen, 2020; Hengelo, 2020; Leeuwarden, 2020; Heath, 2009; Hendricks & Calkins, 2006; Sanyé-Mengual et al., 2016; Leiden, 2020). In Germany, at least 48 cities provide financial support Sarwar & Alsaggaf, 2020; Specht & Sanyé-Mengual, 2017; Specht, Sie­ (Technical and Environment Administration Copenhagen, 2016) that bert, & Thomaier, 2016; Zhang et al., 2012). Table 1 presents some primarily covers 50% to 60% of the green roof cost (Berardi et al., 2014; studies conducted to identify barriers and opportunities for imple­ Grant, 2018). menting GR and RUA from the point of view of stakeholders or citizens. In the United States (USA), many cities (Austin, Baltimore, Mil­ The system studied included rooftop greenhouses (RTGs), rooftop waukee, Minneapolis, Philadelphia, New York City (NYC), Portland, open-air farming and urban rooftop farming (URF), all possible types of Seattle, and Washington) offered financial support (Berardi et al., 2014). urban agriculture in and on buildings (ZFarming), and urban agriculture For example, Chicago supports up to 50% of the cost if the green roof (UA*), including rooftop agriculture and green roofs (GR). Data collec­ covers greater than 50% of the net roof area (Adaptation Clearinghouse, tion was performed using interviews (I), seminar of discussions (S), and 2015; Berardi et al., 2014). questionnaires (Q). Participants from studies included stakeholders Singapore encourages the installation of green roofs by subsidizing already actively involved in green roofs or rooftop agriculture projects up to 50% of the cost for both residential and commercial buildings; (AS), stakeholders not actively involved but considered important due to green roofs must be maintained for at least five years after construction their knowledge (NAS), and citizen or residents (C). (Singapore Government, 2020). As reflected in Table 1, the most frequent methods used for data Some cities in North Europe have approved changes in building, collection included interviews and questionnaires; most of these studies construction (e.g., Basel, Berlin, Stuttgart, and Copenhagen) and land- included different and multidisciplinary participants specialized in use planning codes (for example in London) to require bylaw green diverse fields, including city planning, construction, public administra­ roofs. At the country level, France integrated a national law to require tion, research centers, agronomy, food distribution, sales, associations, 2 P. Zambrano-Prado et al. Cities 114 (2021) 103196 Table 1 Studies of barriers and opportunities from stakeholders’ perceptions. City System Data collection Participant Key approach Reference I S Q AS NAS C Barcelona (Spain) RTGs ● ● Barriers and opportunities (Cerón-Palma et al., 2012) Barcelona (Spain) URF ● ● ● Barriers and opportunities (Sanyé-Mengual et al., 2016) Berlin (Germany) ZFarming ● ● ● Benefits and risks (Specht, Siebert, & Thomaier, 2016) Berlin (Germany) and Barcelona (Spain) URF ● ● ● Risks (Specht & Sanyé-Mengual, 2017) Bologna (Italy) UA* ● ● Social acceptance (Sanyé-Mengual, Specht, et al., 2018) Chicago and Indianapolis (USA) GR ● ● ● Cost, benefits, barriers, and incentives (Hendricks & Calkins, 2006) Hong Kong (China) GR ● ● ● ● Barriers (Zhang et al., 2012) Lahore (Pakistan) GR ● ● Motivation to adopt GR (Sarwar & Alsaggaf, 2020) Texas (USA) GR ● ● Barriers and facilitators (Heath, 2009) and activist institutions from both private and public institutions Worldwide, GR and RUA are increasingly used in cities, primarily as (Heath, 2009; Sarwar & Alsaggaf, 2020; Specht & Sanyé-Mengual, 2017; a part of air quality, climate resilience, and biodiversity strategies. Specht, Siebert, & Thomaier, 2016). In contrast, other works focused on Various policies and regulations in promoting green roofs and rooftop developers, city officials, and architects (Heath, 2009; Zhang et al., agriculture have been developed and introduced in North Europe 2012). Citizen and residents perceptions also have been the center of (particularly Germany and the Netherlands) and North America. These studies (Hendricks & Calkins, 2006; Sanyé-Mengual, Specht, et al., contexts represent cases with cold winters and fewer sun hours 2018; Sarwar & Alsaggaf, 2020). Perspectives focused on building compared with other regions, such as the South of Europe where climate owners and architects (Hendricks & Calkins, 2006) are minimally conditions are more favorable for rooftop agriculture production reported. (Sanyé-Mengual et al., 2016). Studies that consider data collection methods where stakeholders On the other hand, regarding case studies, the literature indicates a interact and share their knowledge and experiences (e.g., focus groups, high potential of roofs (2608 ha) suitable for GR and RUA imple­ Knowledge network, or World Café) to address barriers and opportu­ mentation in Barcelona city (Urban Ecology Agency Barcelona, 2010). nities regarding the implementation of GR and RUA projects are lacking. Even with this potential, currently only the 0.36% of Barcelona’s roofs are GR and RUA (Urban Ecology Agency Barcelona, 2010). 1.4. World Café method Previous works show a lack of policies and incentives to encourage GR and RUA projects in Barcelona; however, the recent Climate Plan World Café is based in a constructive conversation related to critical 2018–2030 considers GR and RUA implementation to mitigate and questions and collaborative learning. It assumes that the knowledge that adapt to climate change and improve the quality of life (Barcelona City we are searching is already present (Fouché & Light, 2011). This Council, 2018). In this sense, the municipality of Barcelona recently participatory method is particularly powerful due the informal envi­ started to encourage these types of facilities through the first contest ronment, and its structured dialogue focuses on questions relevant to the called The First Green Roofs Contest. In this sense, the incentives for participants and promotes rounds of information exchanges between the these projects appear to be very recent compared with other geographic stakeholders that results in a cross-pollination of ideas (Estacio & Karic, regions. 2015; Fouché & Light, 2011; Prewitt, 2011). This method has been used Few studies have examined barriers and opportunities of GR and in a variety of settings to identify and analyze barriers and opportunities RUA projects in Barcelona, and these works were performed before the and other research aspects. For example, in London, the method was first subsidy initiative was launched. Furthermore, data collection was used as one part of “Well London”, a five-year program to promote the performed by interviews, and discussions were held in seminars. These health and well-being of their residents (Bertotti et al., 2012). In addi­ methods have some limitations for generating insights from participants tion, the method has been used in deprived urban neighborhoods to about their knowledge and experiences. Other methods, such as the analyze how residents view ‘community’ and the barriers to community World Café, can be used as a platform to gather collective knowledge to cohesion (Bertotti et al., 2012). The method has been used in higher address these types of subjects. education to encourage reflection on internationalization (Estacio & For this work, the term urban agri-green roofs (UAGR) will be used to Karic, 2015). In Ireland and the USA, the method was used for priori­ refer both green roofs without and with horticulture activities consid­ tization of marginalized communities (MacFarlane et al., 2017). In ering open-air as a production system. Genova, it was used to identify potential areas of research for measuring The study makes relevant contributions with respect to previous sustainability performance (Silva & Guenther, 2018). World Café was research in this field. First and contrary to most barriers-opportunities employed in secondary school classrooms to identify barriers and op­ studies and policies developed in North Europe and North America, portunities to implement an educative program (Cosby et al., 2019). The this research focuses on Southern European, where incentives to support method was also used in Ireland to explore barriers and opportunities to UAGR have recently emerged. For this reason, the contributed findings enhance research among pharmacists (Kavanagh et al., 2020). are important to provide a solid basis for the policies that aid in the In this study, the World Café technique was chosen to elicit barriers development of sustainability in cities moving towards the imple­ and opportunities from the stakeholders because this method allows mentation of these policies, such as Barcelona. Second, the use of World participants to share their thoughts and opinions in an open, welcoming, Café is an effective method for collecting data on perceptions of barriers and social environment. Participants feel comfortable in this setting, so and opportunities, but it has not been used on previous research in this method provides an opportunity for mutual insight and innovative Barcelona. Third, this study assessed the personal experience of the thinking and creates possibilities for action (Estacio & Karic, 2015; stakeholders with The First Green Roof Contest and their real experience Fouché & Light, 2011). in the different stages of the project- construction-use process. Based on Additionally, World Café has been used effectively in analyzing the above perspectives, this is a new approach in this field of study. barriers and opportunities (Bertotti et al., 2012; Cosby et al., 2019; Finally, the work explores new perspectives regarding not only the Kavanagh et al., 2020). This method exhibited a significantly higher identification of barriers and opportunities but also the stage of the life positive effect compared with traditional strategy workshops (Chang & cycle (project-construction-use) of UAGR and the scale where barriers Chen, 2015). and opportunities are presented, representing an original and integrated 3 P. Zambrano-Prado et al. Cities 114 (2021) 103196 approach to the topic to be investigated. (1) Mediterranean compact city. According to macro definitions, In this regard, the aim of this research is to identify the perceptions of countries of Southern Europe share some geopolitical and socio­ barriers and opportunities for implementing UAGR projects in a Medi­ economic characteristics (Leontidou, 1990) and advanced socio- terranean compact city. In this sense, the specific objectives are as economic and political realities distinguish by similar urban is­ follows: sues compared with North African and Middle Eastern Mediter­ ranean cities (Pace, 2002). Regarding micro definitions, the (1) To identify potential social, environmental, legal/administrative, typical elements of many Mediterranean cities were defined as technological/architectural, and economic barriers and oppor­ follows: recognizability of urban spaces, the subdivision of tunities for integrating UAGR. neighborhoods, and the continuous mix of architectural typol­ (2) To determine the scale, including building, city, or global aspects, ogies. Mediterranean cities have been affected by similar prob­ of potential barriers and opportunities are presented. lems, such as intensive housing; lack of green areas, (3) To classify the perceptions of potential barriers and opportunities infrastructures, and services; and intensive exploitation of soil within a UAGR project’s life cycle stages: project-construction- (Leontidou, 1990; Pace, 2002). These sharing characteristics use. make Mediterranean cities from Europe countries comparable (Leontidou, 1990). 2. Methods Barcelona is considered worldwide as an example of a compact city (Parés et al., 2013; Rueda, 2007) with 1.6 million inhabitants Five stages were considered to address the work: (1) case study, (2) in 101.3 km2 (15,747 inhabitants/km2), representing one of the participants’ definitions, (3) identification of barriers and opportunities, most dense cities in Europe (Barcelona City Council, 2018). (4) data collection, and (5) data analysis. These stages are described in (2) Lack of green spaces and competition of land. Approximately 20% of detail in the following subsections. Fig. 1 presents the workflow of this the city’s surface is occupied by densely built houses, and the city research. has 17.6 m2 of green surface including Collserola Natural Park per inhabitant. Excluding this zone, the green space per inhabi­ 2.1. Case study tant is only approximately 7 m2 (Barcelona City Council, 2018). (3) Suitable weather. Barcelona has predominant sunny weather The city of Barcelona (Spain) was chosen as a case study based on the during most of the year with average temperatures between 12 following criteria: and 18 ◦ C during the winter and 20–26 ◦ C during the summer (Barcelona City Council, 2018). These climate conditions repre­ sent a good environment for agricultural production. Fig. 1. Workflow to identify potential barriers and opportunities regarding UAGR implementation. Percentage of agreement (a) where p represents the number of stakeholders who identified the same barrier or opportunity and n is the total number of participants in the sessions. Relative weight (rw) expressed in percentage where c is the total times that each barrier or opportunity was mentioned and m the total mentions in each barrier/opportunity category. 4 P. Zambrano-Prado et al. Cities 114 (2021) 103196 (4) Recent initiatives to promote green roofs. Barcelona’s Climate Plan 2.3. Identification of barriers and opportunities 2018–2030 set the following objective: to reach 34,100 m2 of green roofs, walls, and facades by 2030. Some of the short-term Five categories of barriers and opportunities were identified based on actions include to drawing up a bylaw to promote productive the previous literature related to rooftop urban agriculture perceptions roofs and consolidating the annual green roof contest. (Cerón-Palma et al., 2012; Nadal, Oriol, et al., 2018; Sanyé-Mengual et al., 2016; Specht & Sanyé-Mengual, 2017): (1) social, (2) environ­ Within this background, a call of projects for The First Green Roof mental, (3) legal/administrative, (4) technological/architectural, and Contest was made in 2017. Projects could integrate UAGR, rainwater (5) economic. harvesting, and renewable energy systems. However, this study focuses on UAGR issues. The boundaries of the study area comprise Barcelona 2.4. Data collection municipality districts, where the UAGR project winners of The First Green Roof Contest were located: L’Exaimple, Ciutat Vella, Sants Mon­ The data collection was performed using the World Café method tjuic, Sarria-Sant Gervasi, Gracia, Horta-Gunardó, and Sant Andreu. In (The World Café Community Foundation, 2015) by applying the seven this context, this work considers public and private buildings with principles of the method. diverse building uses according to the participant projects, including As a first step, the session began with registration. Each participant housing, educational, offices, health, and industrial uses. was supplied with a label with name and a code according to their stakeholder category. After registration, a welcome presentation was made followed by an explanation of the purpose of the conversation and 2.2. Participants definition how the workshop would proceed. The workshop comprised two sessions (performed in one day) and Participants were persons involved in Barcelona’s First Green Roof five rounds (in each discussion table) by session. The first session Contest. In this sense, participants had recent and updated knowledge of focused on the barriers, and the second session focused on the oppor­ the process of implementation of UAGR (from project to use stages). tunities related with UAGR. A break occurred between each session. Stakeholders were categorized according to two main criteria: 1) the The room was set up with five discussion tables; each one focused on specific role that they play in the stages of the project’s life cycle one specific barriers/opportunities category. Participants were orga­ regarding the implementation of UAGR, (a) project, (b) municipal nized into five groups (participants chose the table where they wanted to licenses and urban planning, (c) construction/deconstruction, and (d) start) composed of between 4 and 5 people and one host. use and tracking; and 2) their provenance, including (a) private com­ panies (PC), (b) public administrations (PA), (c) research centers (RC), and (d) owners and users (OU). Fig. 2 shows categorization of participants. 313 314 315 316 317 318 Fig. 2. Stakeholders involved in the stages of a UAGR. 5 P. Zambrano-Prado et al. Cities 114 (2021) 103196 2.4.1. Applying the World Café method principles 7. Analyze and share the results. Findings from the discussion tables were visible for everyone to view and thematically displayed on ta­ 1. Setting the context. The topics were set by the barriers/opportunities bles. Hosts and stakeholders were encouraged to view the collection in the five categories previously identified: social, environmental, of experiences and knowledge. In addition, after data analysis, a legal/administrative, technological/architectural, and economic. plenary session with participants was held, and results were pre­ The workshop was designed to facilitate the sharing knowledge and sented in this session. recent experiences regarding their participation in the contest through multi-directional knowledge exchange by contributing, 2.5. Data analysis connecting, and listening to each other. 2. Create hospitable space. An informal environment with a relaxed Data generated from the discussion tables were thematically orga­ atmosphere was the aim, which was addressed through two main nized and analyzed in Microsoft Excel ®. This process made it possible to aspects: (1) comfortable space and furniture and (2) appropriate preserve the essence and nuances of each contribution while synthe­ facilitators. The room for the workshop was big enough to allow five sizing the ideas under the same barrier or opportunity category. The groups to work comfortably and simultaneously (an events hall of process of data representation involved the following steps: Barcelona’s municipality building). The room was set up in a café style with chairs and tables; the room had a patio with natural light. 1. Identification of barriers/opportunities: social, environmental, Coffee and catering services were offered free of charge during all legal/administrative, technological/architectural, and economic. workshop sessions. 2. Quantification of the total mentions (m) in each barrier/opportunity category: social, environmental, legal/administrative, technolog­ Facilitators were previously trained on the goals and practice of the ical/architectural, and economic. World Café method. Table hosts came from diverse fields related to 3. Quantification of total mentions (c) in each barrier/opportunity green roof projects (one architect, one agronomist, two environmental identified. scientists and one green roof entrepreneur). Most of the hosts had aca­ 4. Percentage of agreement. Eq. (1) was used to obtain stakeholder demic and research backgrounds and practiced in their specific profes­ agreement regarding barriers/opportunities. Where a is the agree­ sional field. ment (%), p represents the number of stakeholders that identified the A welcome to the table discussion and introduction were made by same barrier or opportunity and n is the total number of participants hosts in each round of discussion. in the sessions. a = p/n × 100 (1) 3. Exploring questions that matter. Discussions started with an open question that would identify key barriers and opportunities related to UAGR projects. The same question was discussed in the five tables, 5. Relative weight. Eq. (2) was used to calculate the percentage of but each table focused on a different topic. This setup allowed relative weight (rw) of the barrier/opportunity. Where c is the total stakeholders to explore the related areas around a question. The mentions in each barrier/opportunity, and m corresponds to the total following question was discussed: mentions in each category of barrier/opportunity. rw = c/m × 100 (2) What are the barriers or opportunities (according to the session) related to UAGR projects? Each round of discussion lasted 15 min. Once the designated time 6. Categorization of the scale of impact. This step refers to the specific expired, the participants in each table were asked to rotate and form new area where each barrier or opportunity is presented. For this crite­ groups to discuss other topic; stakeholders participated in all discussion rion, three main scales were distinguished: building (B), city (C), and tables with different groups. If during the discussions, no contributions global (G). A scale was assigned to each barrier and opportunity. were made, a list of barriers and/or opportunities and based on the 7. Categorization of the stages of UAGR project’s life cycle. This step literature was prepared in advance and was offered to those attending to refers to the specific stage of the complete implementation of the boost the discussion (see supplemental information). UAGR process at which each barrier and opportunity appears. For this criterion, three main stages were distinguished: project (P) if the 4. Encourage everyone’s contribution. The principal aim of the table barrier or opportunity appears during the design; construction/ host was to facilitate dialogue, welcome each new group of partici­ deconstruction (C) if the barrier or opportunity appears during the pants, introduce them to the topic being discussed, and ensure that process of mounting or disassembling the UAGR; and use (U) if the everybody’s voice and ideas are heard. No limit in the number of barrier or opportunity appears once the UAGR has been built and has interventions discussed by a participant was set. a relationship with its operation. 5. Connect diverse perspectives. This principle was developed to pro­ vide a continuity of ideas from the table hosts who remained in the 3. Results and discussion same table and used the provided notes of the previous group(s) to provide them with input into previously discussed topics. 3.1. Identification of barriers and opportunities 6. Listen together for patterns and insights. The host encouraged par­ ticipants to listen and pay attention to others’ opinions. At the The seminar was attended by 70% of the invited actors (24 out of conclusion of the question, participants shared their insights and 34). As mentioned above (Section 2.2), the segments of the participation thoughts about collective patterns of knowledge. were divided according to the role played by the stakeholders in the UAGR projects: 11 belonged to private companies (PC), 5 were involved The method used aims to capture the participants’ views and in­ in public administration (PA), 4 were members of research centers (RC), sights. In this sense, the goal was to be as non-disruptive as possible and 4 attended as building owners and users (OU). However, during the while simultaneously helping to maintain the informality and café-like session, some participants left discussion tables about the economic atmosphere in the room. The host at each table recorded the responses barriers for personal reasons. Thus, the number of participants in this and added notes of the narratives provided by the participants. category were as follows: n = 22 (barriers) and n = 18 (opportunities). During data collection, it was not necessary to use the barriers and opportunities support list for the World Café by categories (see the list on 6 P. Zambrano-Prado et al. Cities 114 (2021) 103196 supplementary information) prepared to boost the discussion. A total of 3.1.1. Social barriers and opportunities 59 barriers (z) were identified: 13 social, 12 environmental, 15 legal/ The notable social barriers perceived by the stakeholders with administrative, 6 economic, 13 and technological/architectural. A total consensus among all the actors were (1) the need of information and of 70 opportunities (z) were detected: 22 social, 13 environmental, 11 scope of UAGR projects, such as prejudices, skepticism, lack of running legal/administrative, 11 economic, and 13 technological/architectural. examples and sensibility, little or no support by the municipality or the Fig. 3 presents a summary of most mentioned barriers and opportunities feeling that agri-green roofs will bring more problems than benefits, and in each category and their relative weight. The total number of mentions (2) the lack of social cohesion, including low involvement of the com­ (t) was 317 for barriers and 297 for opportunities considering all bar­ munity members in the implementation of these types of projects. Both riers and opportunities categories. For full data see the table complete barriers represent 44% of the total contributions in this area. barriers and opportunities data extracted from the UAGR seminar from the The lack of information about the real scope of UAGR projects in­ supplementary information. cludes the fact that fears and prejudices against such a project can in­ The total mentions in each barriers category (m) were as follow: 110 fluence more than the potential benefits, such as performing major social, 74 legal/administrative, 64 technological/architectural, 44 work, water, and humidity or the influence of pollution on agricultural environmental, and 25 economic. The total mentions in each category of products. The absence of spirit and social cohesion affects the “project” opportunities were as follows: 117 social, 55 environmental, 48 legal/ stage insofar as the lack of predisposition by users and owners of administrative, 40 technological/architectural, and 37 economic. Result buildings makes it difficult to implement UAGR projects. According to showed that not all barriers/opportunities categories have the same the registered opinions, such lack of spirit is not considered to be due to number of mentions. The category that generated more mentions was skepticism but rather various concepts, such as “social good” or “citizen the social category with a total of 227 considering both barriers and awareness”. Specifically, these concepts suggest that the priority of the opportunities, whereas the economic category generated the least collective interest against the individual is not well-integrated in city comments with a total of 62. communities. Tables 2 and 3 present the most mentioned barriers and opportu­ Another barrier is the doubt about whether these spaces will be used nities based on their relative weight, stakeholders’ agreement, scale, and (75% of agreement). This issue is not unanimously perceived by any stage of UAGR life cycle. type of actor; however, in each category, someone identifies this barrier. Future maintenance problems (46% of agreement) are also an important Fig. 3. Summary of most mentioned barriers and opportunities regarding the UAGR Barcelona case study. Here, t represents the total number of mentions considering all barriers/opportunities categories, and z represents the total barriers/opportunities identified. 7 P. Zambrano-Prado et al. Cities 114 (2021) 103196 Table 2 Barriers regarding UAGR implementation in the city of Barcelona. If a barrier was unanimously identified among all the stakeholders of the same type, it is rep­ resented in dark grey. If the barrier was identified by some stakeholders but not all, it is noted in light grey. If the barrier was not identified by stakeholders, it appears blank. Stakeholders were public administration (PA), private companies (PC), research centers (RC), and owners and users (OU). Scale includes city (C), building (B), and global (G). Stage of UAGR life cycle comprises project (P), construction (C), and use (U). concern. found in previous studies where the social cohesion was perceived only Consumers’ lack of trust in the quality and health risks of producing as an opportunity. food on rooftops represents the principal social barrier reported in some Regarding social opportunities, several proposals were observed as cities, including Bologna (Sanyé-Mengual, Orsini, & Gianquinto, 2018) well as numerous nuances when discussing the perceptions described and Berlin (Specht, Siebert, & Thomaier, 2016; Specht, Weith, et al., under one opportunity topic. The only social opportunity that generates 2016), as it is a new model of food production and there is an absence of an absolute consensus in its perception among all the stakeholders was information about how it performs in relation to air pollution in urban “social cohesion”; however, the relative weight of the responses was areas. This perception is related to prejudices and skepticism, which is lower than that noted for barriers (16% of the total opinions versus one of the principals (lack of information and scope regarding UAGR) 22%). In this sense, under the umbrella of the opportunity mentioned, social barriers identified in this study. A recent study related to air the actors perceive that UAGR could offer the possibility to generate new pollution in rooftop crops shows that heavy metal concentrations in rules and attitudes as well as the possibility of benefiting specific groups lettuce are less than the EU-legislated level even when the lettuce crops of users and offering new spaces for citizen participation at all levels (for grown using open-air growing systems were located in high-traffic areas example, geriatrics, schools, individuals, or families). of Barcelona (Ercilla-Montserrat et al., 2018). Another widely perceived opportunity (68% of stakeholders) corre­ The previous studies identify low acceptance and concerns related to sponds to the possibility of creating community garden spaces, which rooftop food production using soil-less growing systems, which is was accepted by all participants related to the fields of research (RC) and perceived as “artificial, unnatural, and not real” (Sanyé-Mengual et al., private companies (PC). Educational opportunity emerges with the same 2016; Specht & Sanyé-Mengual, 2017). However, this barrier was not percentage of perception although with a slight variation in the distri­ mentioned in the results of the seminar. A positive perception was re­ bution among stakeholders. In this category, the richness and variety of ported in a previous study in Barcelona (Ercilla-Montserrat et al., 2019). references that we could classify as the same barrier were remarkable. It In this sense, it is important that Municipalities develop programs to should also be noted that social cohesion was also perceived as a barrier disseminate appropriate information about UAGR crop systems and the (as lacking) and as an opportunity (as UAGR can offer new spaces and quality of the products to the stakeholders, which could be reflected in methods to generate it). Another important detail corresponds to the fact the gradual decrease of this shared social barrier in various European that many of the mentioned social barriers and opportunities are not cities. “purely” social but are very interrelated among other categories (socio- In Berlin, a social perception was identified, namely that this type of economic, legal, administrative, and environmental). project is exclusive and acts as a driver for gentrification (Specht, Sie­ Regarding social opportunities, this study and previous studies from bert, & Thomaier, 2016). In NYC, noteworthy discrepancies in obtaining Barcelona, Bologna and Berlin identified social cohesion and education assets in the UA framework were noted, this generate inequality for UA as major benefits of the integration of UAGR projects (Cerón-Palma projects (Cohen & Reynolds, 2015). Gentrification is also a concern and et al., 2012; Sanyé-Mengual et al., 2016; Specht, Siebert, & Thomaier, a paradox of urban greening (Cole et al., 2017; Specht & Sanyé-Mengual, 2016). In this sense, UAGR emerged as a catalyst for community 2017; Wolch et al., 2014). These perceptions were not mentioned in the improvement and social interaction. In addition, UAGR the strength­ World Café conducted in Barcelona. However, this study revealed a new ened social ties and served as an educational tool and a major means of concern about the lack of social cohesion; this social barrier was not appreciating local products (Cerón-Palma et al., 2012). In discussing 8 P. Zambrano-Prado et al. Cities 114 (2021) 103196 Table 3 Opportunities regarding UAGR implementation in the city of Barcelona. If an opportunity was unanimously identified among all the stakeholders of the same type, it is represented in dark grey. If the barrier was identified by some stakeholders but not all, it is noted in light grey. If the barrier was not identified by stakeholders, it appears blank. Stakeholders were public administration (PA), private companies (PC), research centers (RC), and owners and users (OU). Scale includes city (C), building (B), and global (G). Stage of UAGR life cycle comprises project (P), construction (C), and use (U). barriers and limitations, we found connections with the possibility of However, this barrier was not identified by any of the actors corre­ low user acceptance and social indifference; however, the lack of qual­ sponding to the owners and users (OU) category. ified personnel to take advantage of the educational potential, the in­ The major environmental barrier identified in the seminar was Bar­ compatibility of UAGR with city activities, and the loss of rural jobs or celona’s climate conditions. This result had no relationship between the social disparities about the accessibility to the production systems were environmental barriers reported in the previous works (e.g., Cerón- not perceived as barriers in the seminar. Otherwise, the lack of infor­ Palma et al., 2012; Sanyé-Mengual et al., 2016; Specht et al., 2014), mation and scope of UAGR, which appear as the most important barriers which could be attributed the participants in this study who interpreted in this study, are not reported in previous works. the environmental concept in relation to the climate and natural resource conditions for growing food rather than environmental im­ 3.1.2. Environmental barriers and opportunities pacts. The major environmental concerns in the previous research were In the environmental field, less concordance is found among stake­ related to the environmental impact of construction materials (Sanyé- holders compared with the social field. Thus, only one barrier, the Mengual et al., 2016; Specht & Sanyé-Mengual, 2017; Specht, Siebert, & Mediterranean climate, exhibits greater than 50% agreement among Thomaier, 2016). Health risks due to air pollution, low expected quality shareholder categories, and only two (Mediterranean climate and the products (Specht, Siebert, & Thomaier, 2016), and problems regarding uses and quality of water) generated consensus among all stakeholder organic waste management (Cerón-Palma et al., 2012) were not categories. mentioned in the seminar. Mediterranean climate obtains the specific weight of 30% with With respect to opportunities, the heterogeneous tendency remains, respect to total responses in this category, and it is identified by all and no clear opportunity was perceived in four of five categories by stakeholders’ categories. However, none of them identified it unani­ participants. The category with the greatest percentage of acceptance mously. Mediterranean climate is identified as a barrier regarding the (improved life quality) does not reach 50%, and it has a relative weight form and frequency of precipitation, which occurs in sporadic but of 16%. The next highest category of acceptance has a relative weight of intense events (storms) with sun effects and wind. The uses and quality 11% and 32% agreement. “Environmental education” was only of water were also perceived as a barrier for all stakeholders although perceived by stakeholders from public administration and private with less agreement and relative weight (29% and 16%). The barrier of companies. lack of technical or/and environmental training exhibits the same per­ It should be noted that opportunities regarding climate change centage as the uses and quality of water. This limitation refers to the lack mitigation, reduction of UHI effect, energy savings, and improvements of knowledge by the stakeholders involved in UAGR projects in various in thermal and acoustic insulation were very residual (none exceeds 7% relevant topics, including bird migration and the selection of vegetation relative weight). or species that should be introduced to preserve ecosystem equilibrium. In addition, carbon footprint reduction and reduction impacts 9 P. Zambrano-Prado et al. Cities 114 (2021) 103196 associated with transport (Cerón-Palma et al., 2012) were identified create laws and programs to promote and increase UAGR projects. The under the improved air quality opportunity, as does biodiversity experience of cities that have changed policies concerning the integra­ improvement (Williams et al., 2010). This is in keeping with the general tion of UAGR projects show the potential that Barcelona now must perception that there is a clear lack of information about the scope and change the law towards regulations that are more friendly to UAGR effects of UAGR within the population. projects. Thus, some legal initiatives have emerged in Barcelona. Regarding water management, policies from North Europe, required Beginning in 1999, the Ordinance of Urban Landscape of Barcelona water retention capacity at list from 15 l/m2 to 30 l/m2 depending on authorized planters and pots on rooftops as long as they are mobile. the municipality to obtain a subsidy (Almelo, 2020; Amstelveen, 2019; Later, in 2013, the Barcelona Green Infrastructure and Biodiversity Plan Amsterdam, 2020; Den Bosch, 2020; Groningen, 2020; Hengelo, 2020; advocated for the promotion of urban green zones on rooftops. In 2017, Leeuwarden, 2020; Leiden, 2020). the Stimulus Programme for the City’s Urban Green Infrastructures proposed an increase of 1 m2 of urban green areas per inhabitant by 3.1.3. Legal/administrative barriers and opportunities 2030, taking rooftops into account. In 2018, within the framework of the In terms of legal and administrative barriers and opportunities, more Climate Plan 2018–2030 for Barcelona (the research of this paper is in consensus was found among the stakeholders compared with the envi­ fact part of this green infrastructure promotion plan by the city council), ronmental field. Within the barriers, the lack of specific regulations and several proposals were introduced, such as laws to promote productive protocols regarding UAGR was remarkable with 71% of agreement rooftops, boost the energy generation on rooftops and promote water among actors, 23% relative weight and unanimous identification by the collection and use in buildings. There is a need to assess the regulatory four types of stakeholders. However, this barrier was only identified by barriers of UAGR projects to encourage food production on rooftops all the individuals in the public administration group. Some in­ within each city and explore the use of incentives to encourage these terventions recorded during the seminar referred to criteria disparity, projects, providing advantages in the local economy and social benefits differences in legislation interpretation or lack of stability; these find­ and mitigating environmental impacts. ings coincided with those reported by Specht, Siebert, and Thomaier (2016) where stakeholders from Berlin perceived numerous un­ 3.1.4. Economic barriers and opportunities certainties and regulatory gaps. The discussions of economic barriers are one of the sections in which Another barrier that stands out is building volume limitation in the there was less participation. Only 25 answers were registered (for 117 in implementation of UAGR (54% agreement and 17% relative weight) as social barriers or 74 in legal barriers), and no barrier reached 50% specific legislation is limiting in terms of structural reinforcement, agreement among stakeholders (Table 2). shadow, or greenhouses facilities. Rooftop greenhouses encounter a Taking this lack of engagement into account, the most widely barrier to development as some buildings are at or exceed their floor-to- perceived barrier corresponds to the initial capital investment with 46% area ratio (FAR) allowance, preventing an addition to the building. agreement among stakeholders but a relative weight of 40%. This bar­ Policy changes to facilitate their development have been implemented rier was identified by all the typologies of participants. This barrier re­ in NYC where the Departments of Buildings and City Planning developed fers to the installation and facilities costs, work, and materials, as well as a waiver program for greenhouses seeking space on buildings that have economic disproportion between the necessary structural reinforcement met or exceeded their FAR (The New York City Council, 2010), and and the cost of the UAGR elements. In addition, the rehabilitation of a similar policy changes were recently implemented in Paris (Paris Local roof under a UAGR project can be much more expensive than conven­ Urban Plan, 2018). tional rehabilitation. Stakeholders from this and other worldwide It is also important to mention two more barriers as they are also (Barcelona, Berlin, Chicago, Illinois, and Hong Kong) studies expressed identified by all types of stakeholders although at a reduced percentage. their concerns about the financial issues of UAGR perceiving higher First is the percentage of acceptance of the owners when implementing a investments (Hendricks & Calkins, 2006; Sanyé-Mengual et al., 2016; UAGR in a community of owners. This is an important limiting factor Specht, Siebert, & Thomaier, 2016; Zhang et al., 2012). given that approval by at least 80% of owners is required for a UAGR to Other significant barriers include maintenance costs (not identified prosper. However, for other modifications (such as the installation of an by owners and users) and the low perception of UAGR’s benefits and elevator, for example), 50% is sufficient. The second barrier refers to the advantages given that these factors are perceived as “extra expenses”, difficulties of the legal commercialization of agricultural products and there is minimal interest in investing in it. These findings coincide grown on roofs or regarding urban agriculture. There is a clear identi­ with other studies where maintenance costs have been ranked by fication of regulatory barriers for UAGR projects that is shared with housing project managers as the third most significant barrier in Hong other cities. Kong, the third decision priority by owners and architects from Chicago In the case of Barcelona, its General Metropolitan Plan does not allow and Indianapolis, and one of the most significant barriers identified by agriculture activities inside the city, which makes the commercialization Chicago’s architects (Hendricks & Calkins, 2006; Zhang et al., 2012). of food produced in the city unlawful. There are also height and volume Weak structural loading for integrating UAGR systems as well as in­ limitations regarding the installation of RTGs due to the Spanish Tech­ creases in design and construction cost were also reported by Zhang nical Building Code. et al. (2012). Regarding opportunities, the feedback dynamics that are present in Regarding this fact, the relationships between this barrier and the the previous categories are repeated. Specifically, barriers and oppor­ social barrier of a lack of information and prejudices regarding UAGR tunities were simultaneously identified. This does not mean that the emerged since users are not aware of the potential benefits that the barriers and opportunities coincide but rather that the actions to be implementation of such a project can bring, including economic benefits taken to overcome them are focused on the same field as well as the in the form of savings, for example, in energy bills or the development of opportunities that they present. In this sense, the possibility of devel­ activities and services on the roofs. oping specific regulations for UAGR (79% of agreement and 31% of The difficulty of commercializing the products obtained from UAGR specific weight) emerges as the most widely identified opportunity. appeared in a residual manner during the seminar (4% relative weight). Therefore, UAGR projects open the door to a deep analysis to elaborate Previous studies from Barcelona, Berlin and Bologna (Cerón-Palma upon their own regulations, unify the administration criteria and facil­ et al., 2012; Sanyé-Mengual et al., 2016; Sanyé-Mengual, Orsini, & itate changes in the normative and legal procedures. It must be Gianquinto, 2018; Specht & Sanyé-Mengual, 2017) also identified emphasized that all the stakeholders in the public administration group minimal or no perceived economic benefits as a strong barrier together identified this opportunity, whereas no one in the research centers did. with the fact that it is difficult to develop a rooftop business (connected As we have shown, regulatory barriers are potential opportunities to with legal issues), which some authors (Palmer et al., 2016; Specht & 10 P. Zambrano-Prado et al. Cities 114 (2021) 103196 Sanyé-Mengual, 2017) have also identified as a prominent economic identification of architectural barriers and opportunities is lacking. In barrier together with the competition of UAGR with other rooftop uses. this sense, this study may make an important contribution to this spe­ In terms of opportunities, the profits derived from the new uses of the cific issue. roofs clearly stands out to profit economically from a space that was Regarding opportunities, it is remarkable that none are identified by previously not associated with any pecuniary use. This opportunity all types of stakeholders. This notion is reflected in the low percentages stands out above the others with 67% agreement among stakeholders, of agreement among actors. Thus, no opportunity reaches 50% agree­ 32% relative weight and identification by all types of actors. Within a ment, and the highest percentage is 31%. Thus, the most perceived “direct profit” perspective, a multitude of business opportunities is opportunity (with 32% agreement and 15% relative weight) corre­ found for the community and/or construction companies that incorpo­ sponds to the possibilities of aesthetic improvement offered by UAGR rate UAGR with possibilities, such as renting the space, guided tours or project implementation, including the development of architects’ crea­ holding events, potential food and rainwater harvesting, renewable tivity, developing new “beauty” and “urbanity” concepts within the city energy production/self-consumption and the production and possible or the possibility of “hiding” pre-existing facilities/machinery on the sale of resources. The reduction of costs related to food production, roofs. However, this opportunity was only identified by the actors consumption, and distribution; savings in energy bills; and the switch of belonging to public administration and private companies. the production chain to a more local scale represent indirect opportu­ New space uses and the possibility to update current installations nities identified in the seminar. were perceived with similar agreement and relative weight (26% and Other highlighted opportunities in terms of the percentage of 12%, respectively). In addition, although the numbers are lower than agreement and relative weight include the added value for the building those noted in the first mentioned opportunity, their acceptance among (revaluation), the possibility of creation of new companies and jobs or the types of actors is extensive given that only stakeholders belonging to the commercialization of local products and/or services. However, for research centers do not identify them. The new uses of space include the all these opportunities, the perception among the stakeholders is very possibility of creating quality and comfortable areas, the use of heterogeneous. Participants in the field of public administration (PA) underutilized spaces or responding to new spatial needs. Further, the and private companies (PC) are very receptive, whereas those involved possibility of updating current installations includes the detection and in research centers (RC) or owners and users (OU) are less receptive. amendment of hidden deficiencies as well as improvement in the current When discussing economic opportunities, it is important to note the state of the roofs. double-stranded character presented by the participants. In this sense, The relationship between architectural/technological and environ­ employment opportunities cannot imply a significant number of livable mental opportunities is also noteworthy as many proposals in the wage jobs, and they even require additional expertise. Furthermore, the architectural field have a direct impact on the environment. In this increased value added to the buildings can lead to the displacement of sense, for example, the opportunities to cities and buildings that are low-income residents. more sustainable, such as improvements to thermal and energy insu­ Short-term business opportunities may imply unproven profitability lation or the possibility of creating green corridors, were identified in in the long-term along with indispensable financial and political sup­ both categories. Special mention should be given to the “construction” port, which is not always assured (Palmer et al., 2016). The economic stage, which only presents four technological/architectural barriers and feasibility of these projects must be assessed on a case-by-case basis one barrier regarding legal/administrative issues, and no opportunities (Freisinger et al., 2015). of any type were identified. 3.1.5. Technological and architectural barriers and opportunities Two architectural and technological barriers stand out. First, the 3.2. Barriers and opportunities scale: building, city or global previous situation of the elements on the roof was identified as a barrier with 62% agreement among stakeholders and 23% relative weight. This Fig. 4 illustrates the results related to scale. The overall results barrier refers to the current uses and pre-existing elements in the roof showed that the barriers and opportunities identified by stakeholders that constrain adaptation for new UAGR uses, such as air conditioning during the seminar were mainly distributed between “city” (47%) and facilities, TV aerials, photovoltaic panels, or gardening elements. The “building” (44%), whereas “global” remains at 9%. Regarding barriers, second barrier, which is interrelated with the legal field, is the building’s the data from the seminar reflect that 45% belong to “city”, 46% to load limitation with 58% agreement and 22% relative weight. Both “building” and 9% to “global”. barriers were identified by all the typologies of the stakeholders but not In terms of categories, “city” is the predominant scale in the legal and unanimously. administrative barriers (approximately 70% of relative weight), The complexity of incorporating food, rainwater harvesting, and whereas the “building” scale (75% of relative weight) is emphasized in renewable energy system flows in buildings; the transportation of inputs the architectural and technological barriers. The remaining present a and outputs of UAGR systems; complications in terms of rehabilitating more homogenous distribution with percentages of approximately 50% existing roofs or the use of polluting construction materials are rarely between “city” and “building”. The “global” scale has minimal impact on mentioned in the seminar. Collectively, these barriers have less than the barriers, reaching only 8% relative weight. 10% relative weight. With regard to opportunities, the “building” scale is still outstanding The third perceived barrier (UAGR accessibility) is not often reported (close to 70% of relative weight) in the technological and architectural in the literature but issues associated with this barrier are extensively field, whereas the “city” scale stands out with 63% relative weight in the studied in the literature (Cerón-Palma et al., 2012; Nadal, Cerón-Palma, legal and administration area. In the economic field, the distribution is et al., 2018; Sanyé-Mengual et al., 2016). Along with these issues, the homogenous with approximately 45% of opportunities pertaining to the risks associated with urban integration, which include conflicts (Specht “city” scale and 36% to the “building” scale. In the environmental field, & Sanyé-Mengual, 2017; Specht, Siebert, & Thomaier, 2016) with the the opportunities are distributed homogenously between the “building” “urbanity” and “agriculture” concepts, animal production, noise and/or and “city” scales (with relative weights of 46%, respectively). smell problems or visual/aesthetic image conflicts, were not mentioned Finally, in the social sphere, more opportunities appear is the “city” in the seminar; however, the possibility of aesthetic city improvement scale at approximately 55% followed by the “building” (35%) and was perceived as an opportunity. Load resistance was identified in this “global” (10%) scales. However, the “global” scale minimally represents and previous studies from Barcelona (Cerón-Palma et al., 2012). 10% of the total perceived opportunities. Additionally, the “city” scale Although the previous literature has referred to large barriers and op­ encompasses 49% of opportunities, whereas the “building” scale oc­ portunities for social, economic, and environmental issues, the clear cupies the remaining 41%. 11 P. Zambrano-Prado et al. Cities 114 (2021) 103196 Barriers Barriers Technological/architectural Technological/architectural Economic Economic Legal/administrative Legal/administrative Environmental Environmental Social Social 0% 20% 40% 60% 80% 100% 0% 20% 40% 60% 80% 100% Building City Global Project Construction Use Opportunities Opportunities Technological/architectural Technological/architectural Economic Economic Legal/administrative Legal/administrative Environmental Environmental Social Social 0% 20% 40% 60% 80% 100% 0% 20% 40% 60% 80% 100% Building City Global Project Construction Use Fig. 4. Scale of impact of potential barriers and opportunities regarding UAGRs in the city of Barcelona. Fig. 5. Stage of UAGR life cycle where potential barriers and opportunities emerge regarding UAGRs in the city of Barcelona. 3.3. Barriers and opportunities within UAGR projects life cycle stages urban and building codes by considering the particularities of Regarding the stages of a UAGR life cycle, it is essential to highlight local development plans. the clear division between barriers and opportunities (Fig. 5). Referring (2) For existing buildings, it is generally more difficult to integrate to the barriers, the “project” stage stands out compared with the UAGR according to buildings preconditions. In this case, the remaining stages (62% relative weight). Next, we find the “use” stage integration of incentives should be flexible, and several options (29%) followed by the “construction” stage (9%). Thus, only the envi­ must be developed, for example tax reduction subsidies or call for ronmental category presents a predominance of the “use” stage in the projects with financial support. An example of such incentive is discussions of the barriers, whereas barriers in the other categories determining the subsidy amount per each constructed square (technological/architectural, legal, economic, and social) are clearly meter or a percentage of the total construction costs. It is project based. important to create a simple structure of the offered incentives Within the opportunities, the distribution changes radically, and a and clearly establishing what the project should encompass and clear predominance of the “use” stage emerges with 84% relative weight the minimum requirements to be eligible to apply. of the total of opportunities. The “project” stage presents 16% relative (3) For the practice of food production on rooftops, the following weight, whereas no opportunity is identified at the “construction” stage. legal issues must be addressed: Thus, until UAGRs are in operation, most opportunities are not perceived (or they simply do not appear until the UAGR is completely • A flexible land-use that allow agricultural activities in cities must be operational). This finding leads us to consider why it is difficult to considered by urban planners. perceive UAGRs’ benefits given that without any or fewer UAGR pro­ • Trade of products must be allowed with accurate production and jects in operation, the population will never be aware of its implications distribution regulations. and advantages. • In the case of RTGs, it is necessary to develop a more comprehensive law to allow this type of infrastructure. Regarding the volume and 4. Takeaway for practice floor area permitted in building codes and restrictions for building heights regulations should be flexible to support rather than act as a Policies for integrating UAGR projects should be an interlinked sys­ barrier. tem of laws on national, regional, and local levels and connected with legal regulations regarding construction, resource management, com­ (4) Financial incentives should not be assigned exclusively to the mercial, and urban planning. Based on the results of this work, some stage of UAGR construction. The stage of use is extremely practice and policy recommendation are described: important. However, it requires maintenance works, and a sub­ sidy plans for maintenance costs should be considered. (1) Planning authorities must consider UAGR projects in their na­ (5) Policies also can encourage other environmental goals through tional and local plans to encourage UAGR on new buildings and UAGR projects. A minimum requirement and a type of score achieve UAGR projects through new policies and modifications in ranking can be developed to offer more subsidies or incentives 12 P. Zambrano-Prado et al. Cities 114 (2021) 103196 according to the solutions integrated in the projects regarding recent infrastructures and the most critical point was to identify all goals in specific locations or circumstances, for example: possible limitations and opportunities regarding agri-green roofs in Barcelona, intending to transform these projects in long-term successes • Stormwater runoff mitigation by water retention capacity. and help other cities in possible drawbacks they can find to implement • Rainwater use by collecting rainwater from rooftops. them in their cities. For these reasons, for future studies, we recommend • Integration of renewable energy by including photovoltaics, solar carrying out a sustainability assessment regarding agri-green roofs. thermal panels, or wind turbines. It would also be appropriate to generate more consensus and social • Social cohesion by including spaces designed to create community cohesion. One essential means of contributing to this purpose would be activities. to expand dissemination studies on UAGR opportunities and to respond to the main prejudices of potential users. Research to quantify the eco­ (6) To improve education and awareness of UARG functions and nomic, environmental, and performance benefits of UAGR will ulti­ benefits, the following practice are recommended: mately generate interest in potential adopters on the value of this project. The key points that should be evaluated in future work include • Education programs to disseminate appropriate information to resi­ the following: methods to introduce UAGR within current legal frame­ dents, investors, and city policy makers should be integrated in a works and expand on the interest in the impact and sustainability of the municipal campaign in collaboration with academics, research cen­ used materials and the disequilibrium that can be generated in local ters, or specialized companies involved in UAGR projects. ecosystems. • Those who are interested in learning more about the technology Policies regarding development of technology and construction for should have access to UARG demonstration projects. more sustainable buildings as well as educational programs to train • A database of UAGR projects in cities and scientific evidence professionals in the field of sustainable constructions are important to regarding benefits of UAGR projects should be generated. address. Several of the identified barriers have close links to government (7) Regarding the development of technology and training programs, policy insufficiency; thus, there is urgency for policy instruments. Sup­ it is important to create policies to encourage the development of port policies should include various financial opportunities as well as technologies regarding sustainable criteria, such as materials and bylaw requirements, and municipalities should provide technological processes for integrating UAGR projects. Also, it is necessary to information and support for UAGR systems in the construction phase support training policies for professionals specialized in sustain­ and consider incentives for the use stage. ability regarding UAGR design and construction. (8) The development of UAGR projects could cause gentrification. In Funding this sense, it is important that government integrates regulations to avoid it. This research has received financial support from the European Union’s Horizon 2020 research and innovation program under grant 5. Conclusions agreement No 862663. The publication reflects the author’s views. The Research Executive Agency (REA) is not liable for any use that may be This study has allowed for the attainment of a highly instructive made of the information contained therein. This work was supported by picture of the perception of UAGR projects in the city of Barcelona, and the “María de Maeztu” program for Units of Excellence in R&D this information can aid in the characterization of other cities with [CEX2019-000940-M]. similar features. The authors thank Barcelona city council, for its financial support in Because most barriers are perceived in the project stage and oppor­ the “Compromís de Barcelona pel Clima” framework. The authors also tunities are not perceived until the use phase, an effort by the govern­ thank the Spanish Ministry of Education, Culture and Sports for the ment is needed to implement UAGR projects such that the population grant (FPU16/03238) awarded to Susana Toboso-Chavero, to the Na­ can perceive the benefits generated in all areas of society in an accurate tional Commission for Scientific and Technological Research for the manner. fellowship to Felipe Parada (Becas Chile - Folio 72180248), and to the This study highlighted the need for awareness and information ac­ University of Guadalajara (Mexico) for awarding a research scholarship tivities, and these barriers can be solved with targeted information, to Perla Zambrano-Prado. education, and research dissemination of knowledge regarding UAGRS projects benefits among different actors but especially owners and users CRediT authorship contribution statement to promote a better understanding of their potential benefits. To elab­ orate a clear specific regulation regarding UAGR, generating more social Perla Zambrano-Prado: methodology design; investigation; data consensus and cohesion along with economic support for those projects collection; writing original draft, review and editing; and visualizations. will be critical in facilitating its implementation. Moreover, despite the David Pons-Gumí: methodology design; data collection; formal extensive list of barriers and opportunities, their relative weights are analysis; writing original draft. concentrated, exhibiting minimal dispersion. These features would Susana Toboso-Chavero: methodology design; data collection; facilitate a policy approach in Barcelona. Results can be a reference to writing original draft review and editing; and visualizations. others Mediterranean and compact cities aiming to boost agri-green Felipe Parada: data collection; formal analysis; and visualizations. roofs since they share similar characteristics such as urban forms and Alejandro Josa: project administration and funding acquisition. buildings, and similar issues such as lack of information and specific Xavier Gabarrell: project administration; and funding acquisition. regulations and protocols, social cohesion, and initial investments in this Joan Rieradevall: conceptualization; supervision; and project type of facilities, among other factors. Therefore, this research is an asset administration. towards helping such type of cities to predict and overcome plausible limitations and promoting the opportunities yielded by these projects. Declaration of conflicting interest Considering the focus for future research, it would be appropriate to investigate the development of indicators to monitor the impact of The authors declare no potential conflicts of interest with respect to UAGR to verify how they match the stakeholders’ perception. A the research, authorship and/or publication of this article. constraint for our study was not having enough data to perform a comprehensive sustainability assessment since agri-green roofs are 13 P. Zambrano-Prado et al. Cities 114 (2021) 103196 Appendix A. Supplementary data Fouché, C., & Light, G. (2011). An invitation to dialogue: “The world café” in social work. Qualitative Social Work, 10(1), 28–48. https://doi.org/10.1177/1473325010376016. Freisinger, U. B., Specht, K., Sawicka, M., Busse, M., Siebert, R., Werner, A., … Walk, H. Supplementary data to this article can be found online at https://doi. (2015). There’s something growing on the roof. Rooftop greenhouses. 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